The present invention relates to a music instrument, an excitation device for contact-less excitation of at least one prestressed string by a magnetizable material, as well as to a method for generating sounds.
Known music instruments can, in principle, be classified into two groups, i.e. in acoustical ones and in electric ones, particularly electronic instruments. Acoustical instruments radiate the sound or tone with sufficient loudness so that a piece performed by an acoustical instrument can be directly heard by the audience. For generating and radiating sound acoustical string instruments comprise strings, a tensioning device for the strings and a resonance body, wherein the strings are mechanically started oscillating, the string oscillations are transferred to the resonance body and are radiated by the latter. The various string instruments have each characteristic sounding properties which depend on the strings, the tensioning device, the resonance body and of the mechanical excitation. Electric or electronic instruments generate an electric or electronic signal which is supplied to a loudspeaker via an amplifier and is radiated by the loudspeaker. For playing an electric instrument, a bank of keys or keyboard is provided. The keys may release a signal either directly and/or they may excite a physical system, of which at least one parameter is tapped and transformed into an electric signal. Such a physical system may be used for detecting a characteristic of stroke. With synthesizers, there exist diverse possibilities of a signal alteration. In the case of electroguitars and electrobasses, the physical string oscillation is mechanically excited and is picked up by a cartridge (pick-up) and is fed to a loudspeaker via an electric or electronic circuit. For generating electronic sound signals, MIDI-appliances, such as a MIDI-sax, may be used. A MIDI-sax detects, apart from the grip, also the throughput of air and, optionally, a force which acts from the lips onto the mouth piece, particularly onto a reed. The parameters detected enable generating a signal which, apart from tone pitch and the duration of a tone, comprises also the dynamics of loudness and, optionally, further tone properties. The sound quality of an electric instrument will always depend on the circuitry used and the loudspeaker coupled to it.
From document FR 2 313 740, an apparatus is known in which a plurality of prestressed strings of equal length are each excited in a contact-less manner by an electromagnetic exciting element. In order to be able to start the strings oscillating by changing magnetic fields, the strings are formed of a magnetic material. The strings are arranged between two disks, the disks being kept in a predetermined distance to each other by a cylindrical base. Each exciting element is fed by a frequency so that each string is excited and vibrates at its basic frequency corresponding to its respective string tension. For feeding the exciting elements, a multivibrator having an adjustable frequency is used. In order to render the oscillation of a string audible, it is picked up by a pick-up, and the signal, thus obtained, is supplied to a loudspeaker via an amplifier. The sound generated by such an apparatus will result from the superposition of the basic oscillations of the strings. Thus, it is only a sound source rather than an instrument that can be played. In addition, the sound quality is limited by the loudspeaker.
WO 98/28732 discloses an electroguitar, that can be automatically tuned, in which the strings to be tuned are electromagnetically excited whereupon the string tension is adjusted by an automatic tensioning device. Exciting of each string is effected with the frequency of the desired basic oscillation, and the actually resulting string oscillation is picked up by a pick-up so that a signal of adjustment can be determined from the difference between the desired and picked-up frequencies. The amplitudes necessary for tuning are very small. The electromagnetic excitement device starts the strings oscillating at hardly audible oscillations by a simple electromagnet.
EP-A-0 539 232 discloses an approach for a prolonged oscillation period of a mechanically excited string of an electric string instrument. To this end, the frequency of the excited oscillation is picked by a pick-up device. The signal of the pick-up device is amplified and fed to an electromagnetic exciting device, which keeps the string further oscillating. U.S. Pat. No. 5,070,759 discloses also an approach for a prolonged oscillation period of a mechanically excited string. It is suggested to use the exciting device also as the pick-up. In both approaches, the signal used for exciting is originated from the string itself, and for generating an audible sound, the signal picked up is fed to a loudspeaker via an amplifier. The exciting devices described comprise each at least one coil and parts of magnetizable material and/or parts of a magnetic material. Each coil extends over the whole region which comprises the strings. In order to be able to excite the strings sufficiently, coils of thicker wires and elevated numbers of windings are used, as compared with a pick-up. In addition, examples are described in which the density of the magnetic field is different for differently thick and differently strongly prestressed strings. To this end, either the magnetizable material within the coil is sub-divided into different regions associated to the respective strings by slots or different permanent magnets are assigned to the strings. In these known exciting devices, the electromagnetic field used for exciting extends always over the whole region containing all strings. If a signal stems only from one string, merely a small area of the exciting field is used for exciting this string. The efficiency of this exciting device is very small, and only faint excitements can be achieved which are than acoustically radiated through an amplifier and a loudspeaker.
The acoustical as well as the electric music instruments have their respective limitations. In the case of the acoustical instruments, generating sounds is limited to an appropriate operation of the instrument by a playing person. In the case of electric instruments, a limitation is given by using the necessary loudspeaker. By the known exciting devices for exciting an oscillation of the strings by electromagnetic fields only oscillations of small amplitudes are achievable.